asp.net中生成动态验证码代码

//前台

<td align="left">
<asp:Image ID="imgValidateCode" runat="server" ImageUrl="ImageCreate.aspx" Style="cursor:pointer;" onmouseup="RefreshImage()" alt="点击刷新！" /></td>

//验证码生成页

using System;
using System.Collections;
using System.Configuration;
using System.Data;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Drawing;

/// <summary>
/// 程序名称：生成验证码图片
/// 作 成 者：邱佳龙
/// 作成日期：2011-1-18
/// </summary>
public partial class Admin_ImageCreate : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        this.CreateCheckCodeImage(GenerateCheckCode());
    }

    private string GenerateCheckCode()
    {
        int number;
        char code;
        string checkCode = String.Empty;
        System.Random random = new Random();
        for (int i = 0; i < 4; i++)
        {
            number = random.Next();
            if (number % 2 == 0)
                code = (char)('0' + (char)(number % 10));
            else
                code = (char)('A' + (char)(number % 26));
            checkCode += code.ToString();
        }
        Session["CheckCode"] = checkCode;
        return checkCode;
    }
    private void CreateCheckCodeImage(string checkCode)
    {
        if (checkCode == null || checkCode.Trim() == String.Empty)
            return;
        System.Drawing.Bitmap image = new System.Drawing.Bitmap((int)Math.Ceiling((checkCode.Length * 12.5)), 22);
        Graphics g = Graphics.FromImage(image);
        try
        {
            //生成随机生成器
            Random random = new Random();
            //清空图片背景色
            g.Clear(Color.White);

            Font font = new System.Drawing.Font("Arial", 12, (System.Drawing.FontStyle.Bold | System.Drawing.FontStyle.Italic));
            System.Drawing.Drawing2D.LinearGradientBrush brush = new System.Drawing.Drawing2D.LinearGradientBrush(new Rectangle(0, 0, image.Width, image.Height), Color.Blue, Color.DarkRed, 1.2f, true);
            g.DrawString(checkCode, font, brush, 2, 2);
            System.IO.MemoryStream ms = new System.IO.MemoryStream();
            image.Save(ms, System.Drawing.Imaging.ImageFormat.Gif);
            Response.ClearContent();
            Response.ContentType = "image/Gif";
            Response.BinaryWrite(ms.ToArray());
        }
        finally
        {
            g.Dispose();
            image.Dispose();
        }
    }
}